1. Field of the Invention
The present invention relates to an image forming apparatus including a latent image carrier and an exposing unit.
2. Description of the Related Art
Conventionally, in an electrophotographic image forming apparatus, a structure has been widely employed in which a latent image is written in by a latent image writing unit such as a laser exposing unit that carries out light scanning of laser light in respect of a latent image carrier such as a photosensitive element charged uniformly. In such an image forming apparatus, the latent image writing unit becomes obstructive to maintenance of the latent image carrier and peripheral devices such as a developing unit and the like arranged in the periphery of the latent image carrier depending on the layout in the apparatus, which sometimes results in worsening the maintainability thereof.
Hence, a method is suggested, in which the operability and the maintainability become excellent by separating an exposing unit from a main body of the image forming apparatus, and a technology is disclosed in which a biasing structure is used for the main body in respect of the positioning accuracy of the exposing unit, which is a problem of the separation (for example, see Japanese Patent Application No. 2006-008716 (Japanese Patent Application Laid-open No. 2007-192894)).
Japanese Patent Application No. 2006-008716 discloses (a) the structure in which an exposing unit is held by a cover frame fixed integrally with an openable/closable top cover, cylindrical shafts to be held that are projected from the exposing unit (casing) are allowed to penetrate through openings of the cover frame, respectively, and each of the shafts to be held is allowed to abut both “the bottom wall and the right side wall of the through opening” at the same time and is biased by an extendable bias coil spring, and (b) the structure in which the bottom wall and the right side wall of the through opening of the cover frame are made of a compressible buffer member, and an impact is eased by compressing and deforming the buffer member even when the shaft to be held collides vigorously against “the bottom wall and the right side wall of the through opening”.
Furthermore, when the top cover is closed, the shafts to be held that are biased by the bias coil spring are provided to the side boards of the main body and come into contact with “the positioning unit” that controls the move of the shafts to be held, thereby positioning the exposing unit. That is, in a state of the top cover open, each of the shafts to be held that is biased by the bias coil spring can come into contact with “the bottom wall and the right side wall of the through opening of the cover frame”; however, when the top cover is closed, “the bottom wall and the right side wall of the through opening of the cover frame” with which the shaft to be held has contacted until then retreat farther than “the positioning unit”, and therefore, the shaft to be held directly comes into contact with “the positioning unit”.
When the image forming apparatus is conveyed, the top cover thereof is closed, and therefore the shafts to be held (the exposing unit) directly contact with the positioning unit (the main body) in a state in which the shafts to be held are biased by the biasing force of the bias coil spring. When vibration is generated at the time of conveyance, there is a fear that the shafts to be held (the exposing unit) and the positioning unit (the main body) directly collide against each other, the exposing unit moves owing to the impact, and displacement occurs in the exposure mechanism of the exposing unit.
Further, in respect of attachment of an exposing unit in an image forming apparatus, attachment methods are disclosed. One is that attachment members are provided at three positions in a case in which an optical unit in the exposing unit is housed, the attachment members at the two positions of the three are attached to the main body of the image forming apparatus with the use of fixing members, and the other one is freely supported at the other position (for example, see Japanese Patent Application Laid-open No. 2001-100494), another is that, in respect of support of a writing unit frame that holds an exposing unit, the writing unit frame is positioned by the use of a positioning pin, a front side board is attached to the front side, a rear side board is attached to the rear side opposite to the front side board, and the writing unit frame is fixed by fixing screws (for example, see Japanese Patent Application Laid-open No. 2004-45923), still another attachment method is that a damper is interposed to an exposing unit to prevent vibration generated in association with the reciprocating motion of a carriage for sub scanning of document (for example, see Japanese Patent Application Laid-open No. 2005-31584), and the like. In any attachment methods, suggested is no solution for the problem that displacement occurs in the exposure mechanism of each of the exposing units owing to move of the exposing unit by an unexpected impact force of vibration generated at the time of conveyance.